Current Systems of the North Atlantic and the North Sea

RATHER than attempting to give the details of the currents in the different parts of the Ocean (see, for example, (1)2), the object of the present paper is to present in a general way the modern conceptions and underlying principles regarding the water circulation. To anyone wishing to become broadly acquainted with the surface circulation of the waters in the North Atlantic there are available two sources of information. The more detailed one consists of the current charts published in the various countries primarily for the use of seamen. Such information is usually set out in the form of current roses, showing the velocity, direction and frequency of the currents observed in a definite area during certain periods of time. When one merely needs a generalised view of the circulation, this is perhaps somewhat unwieldy and complicated to deal with, and in consequence one probably goes to the alternative source, which is the ordinary geographical atlas or text-book. Here the circulation represented usually consists of a large whirl formed in the south by the Equatorial Current, in the west by the Gulf Stream, in the north by the North Atlantic Current (called by various names), and closed in the east by the Canaries Current. In the middle is a motionless region which includes the Sargasso Sea. Then we have the cold water supplied from the north by the Labrador and East Greenland Currents, forming perhaps a second, smaller whirl south of Greenland. Such attempts at a general picture of the current system are themselves constructed mainly on the basis of the navigational information, of the kind which is set out in detail in the charts prepared to assist seamen. At sea, it is the usual practice to work out each noon the position of the ship, first, by dead reckoning from a knowledge of her course and speed and, second, by means of astronomical sights. The difference between the two positions, if any, is attributed to the set of the current. Obviously, there are many factors here which can introduce error into the estimation of the current. For example, the ship is influenced by wind as well as current, and another factor is the accuracy with which the helmsman maintains the course. Moreover, the weaker and more transient the current is, the greater will be the effect of these errors on the estimation of it. If the current is a strong